1. Field of the Invention
The present invention relates to a heat treatment apparatus, a method for manufacturing an SOI (silicon on insulator) substrate using the heat treatment apparatus, and a method for manufacturing a semiconductor device using the SOI substrate.
2. Description of the Related Art
In recent years, integrated circuits using an SOI (silicon on insulator) substrate where a thin single crystal semiconductor film is formed on an insulating surface, instead of a bulk silicon wafer, have been developed. Since parasitic capacitance between a drain of a transistor and a substrate is reduced by using the SOI substrate, the SOI substrate has attracted attention due to the ability to improve performance of semiconductor integrated circuits.
As a method for manufacturing an SOI substrate, a hydrogen ion implantation separation method is known. An outline of a method for manufacturing an SOI substrate by using the hydrogen ion implantation separation method is described below. First, hydrogen ions are implanted into a silicon wafer by an ion implantation method to form an ion implantation layer at a predetermined depth from a surface. Next, the silicon wafer into which the hydrogen ions have been implanted is bonded to another silicon wafer with a silicon oxide film interposed therebetween. Then, in the following heat treatment, the ion implantation layer serves as a cleavage plane, and the silicon wafer in which the hydrogen ions have been implanted is separated. Accordingly, a single crystal silicon film can be formed over the silicon wafer which is to be a base substrate.
Further, a method has been proposed (for example, see Reference 1: Japanese Published Patent Application No. H11-163363), in which a single crystal silicon film is formed over a support substrate formed from glass by such a hydrogen ion implantation separation method. Further, recently, a technique has been disclosed, where small pieces of single crystal silicon are arranged into a tiled pattern over a glass substrate, as for a manufacturing method of an SOI substrate for an active matrix liquid crystal display (see Reference 2: Japanese Translation of PCT International Application No. 2005-539259).
Since a glass substrate can have a larger area and is less expensive than a silicon wafer, a glass substrate is used as a base substrate, whereby an inexpensive large-sized SOI substrate can be manufactured. A silicon ingot or a silicon wafer which is to be a base material for forming a single crystal silicon layer is generally small compared to a glass substrate. Accordingly, in the case of using a large-sized glass substrate as a base substrate, a plurality of silicon wafers are bonded to the large-sized glass substrate, which is effective in cost reduction.
Meanwhile, heat treatment of the substrate is required in a hydrogen ion implantation separation method. For example, in order to improve the bonding strength, heat treatment using an RTA (rapid thermal anneal) apparatus is proposed, in Reference 3: Japanese Published Patent Application No. H9-260618. In addition, heat treatment using an RTA apparatus is proposed to be performed after separation in Reference 4: PCT International Publication No. 01/28000.
In the case of heating a substrate using a heat treatment apparatus, in general, the substrate is placed on a support disposed in a treatment chamber, and then heat treatment is performed using a heating unit. For example, in the case of using an RTA apparatus, a plurality of lamps which are provided to face the substrate on the support are used as the heating unit.